Title

State-Determinate Foraging Decisions and Web Architecture in the Spider Dictyna Volucripes (Araneae Dictynidae)

Document Type

Article

Publication Date

Winter 2001

Abstract

Foraging behaviors result from dynamic trade-offs made by organisms, incorporating factors such as past foraging success, reproductive effort, and predation risk. But, decision-making by animals occurs with incomplete information about the environment. We examined the relationship of web architecture and foraging decisions in the tangle web-building spider Dictyna volucripes Keyserling, a common spider in North American fields. Tangle webs are constructed over many days, which increases the total material and energetic investment in webs compared to orb-webs that are rebuilt daily. This reduces the profitability of changing web sites for tangle web spiders, making decisions about allocation of resources to foraging within single patches critical. We studied how foraging success affected investment in webs for High Prey spiders, fed two Drosophila daily, and Low Prey spiders, fed half that amount, over a 9-day period. We found no difference in the total area of silk added to webs. Increase in web area was proportional to initial web size in High Prey spiders, all of which increased webs by approximately 50%, despite substantial variation in initial sizes of webs. But, some Low Prey spiders with small initial webs increased web size by 200–300% while others, with large initial webs, invested proportionately little silk in webs. We also compared the effects of web architecture on prey capture of High and Low Prey spiders, under standardized prey density. There was no difference between High and Low Prey spiders in the number of Drosophila captured. We found a significant positive correlation between sizes of webs and prey capture in High Prey spiders but not in Low Prey spiders. We present the hypothesis that web investment by D. volucripes may incorporate information about both previous foraging effort and foraging success.

Publication Title

Ethology Ecology and Evolution

Volume

13

Issue

2

First Page

105

Last Page

113

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